How to combine two different textures into one
This can be done easily with some baking in Blender.
First, join your two object together with CTRL J.
Create UV map for your bake that include both objects.

Then create a new image for your texture bake, create a new material for it, and make sure it's selected.
Then go to the textures tab, create a new texture, and create (or link in) an image; for example, to create a new 4096² texture image for the output:
 

Then go to the Render tab of the Properties editor, and ensure that the Render Engine is set to Cycles (othwerise the Bake panel below will not be available):

In the Bake panel, set the Bake Mode to Textures, and press Bake.

You should get something like this. (of course it will be your textures instead of mine)

Then just save out the image, remove the other material slots and the first UV map, and you should be good!